I think it’s mostly due to her being the world’s biggest hypocrite. She acts all high and mighty toward John, treating him like crap throughout the whole story. John throughout the first part of RDR2 is literally trying to find his purpose in life and how to be a better man for his kid and future wife. Abigail sees none of that, she only sees what John has already previously done to them. Abigail herself however DOESNT CHANGE AT ALL. She wants everyone to change for her but she doesn’t want to change. She’s still the same dumb lady who was an illiterate prostitute that had a baby with a gang member. And now she’s trying to treat John as if he’s all wrong. Hypocrite